The influence of surfactants on the activities of xylanase and cellulase was studied. A variety of surfactants representing various ionic natures (anionic, cationic, and nonionic) were used,including detergents, defoamers, flotation aids for drinking. The activity of the enzymes increased with all nonionic and cationic surfactants studied. Circular dichroism studies indicated that interaction with nonionic and anionic surfactants changes the molecular structure of the enzymes. The results suggest that xylanase and cellulase enzymes can be used advantageously with nonionic surfactants during various processes in the pulp and paper industry. The use of cationic surfactants is preferable over anionic surfactants. If an anionic surfactant must be used together with xylanase or cellulase in a process, the lowest addition is indicated. The findings also suggest that the incubation of enzymes with surfactant prior to an enzymatic treatment may lead to higher efficiencies from enzymes.